Single lever mixer faucets typically include a cartridge that may set the water flow strength and the relative mixture of cold and hot water. The cartridge may include base static plate and a movable plate. The base static plate includes two inlets to allow entrance of hot and cold water, respectively, into the cartridge and a third opening to allow exit of mixed water. The movable plate includes a single opening that in closed position does not overlap any of the inlets, and in open position overlaps at least part of one or both of the inlets. The movable plate is moved with relation to base static plate by a lever of the cartridge. Water flow rate is controlled by moving a handle of the faucet in one plane (herein after the stream strength control plane which tilts the lever of the cartridge.
Reference is now made to FIG. 1A which is a schematic front view illustration of prior art cartridge 140 and handle 110 of a faucet 100, and to FIGS. 1B and 1C which are cross sectional views of faucet 100, in closed and opened positions, respectively, along axis I-I, marked on FIG. 1A. Handle 110 is firmly fixed to lever 120. Lever 120 is rotatable about pivoting point 130. In the closed position, depicted in FIG. 1B, the single opening of movable plate 142 does not overlap any of the inlets of static plate 144. In the opened position, depicted in FIG. 1C, handle 110 is lifted, lever 120 is rotated and movable plate 142 is shifted with respect to the closed position and the single opening of movable plate 142 overlaps at least part of one or both of the inlets of static plate 144. Movable plate 142 and static plate 144 may be made of ceramic material or include ceramic parts. Additionally or alternatively, parts of movable plate 142 and static plate 144 may be made from various materials or from combinations of materials, such as plastic plates, rubber rings, Teflon cylinder etc. Cartridge 140 may include a base plate 146 that has on one facet openings that match the openings of the static plate which change through base plate 146 into circular openings that match the water supply inlets and outlet of the faucet.
Reference is now made to FIG. 2 which is a schematic diagram representing a handle and a lever of a prior art faucet depicted in relation to a Cartesian axes system including axes x and y. Line 210 represents handle 110 and line 220 represents lever 120 depicted in FIGS. 1A and 1B. Lines 210 and 220 are depicted in the opened position of the faucet, axis x is located where line 220 is placed when in closed position and axis y is perpendicular to x axis. When handle 110 is rotated from being perpendicular to x axis to an angle of α (alpha), movable plate 142 is shifted by h=r sin α, where r is the length of lever 120 from pivoting point 230 to the connection of lever 120 to movable plate 142. For small values of α, for example for α values smaller than 30 degrees or 0.52 radians, sin α≈α, and therefore, h is substantially proportional to α. FIG. 3 presents a graph relating h and α of an exemplary prior art faucet. It is apparent that the relation is substantially linear in the depicted range.
One could assume that the flow rate of water would, therefore, be proportional to α, the angle of rotation of handle 110. However, as a result of the dynamics of the water flow, affected by the water pressure at the entrance of the faucet and by the effect of various sizes of openings on the water flow, the flow rate of water is not exactly proportional to the angle of rotation of the handle. This effect is perceived to be grater than it really is as a result of subjective experience of the user. Thus, the flow rate when handle 110 is shifted at 25% of its range of motion from closed position is perceived as very strong. The flow rate when handle 110 is shifted at 50% of its range of motion from closed position is perceived as so strong, that a typical user assumes this flow rate is close to the maximal available flow rate. The level of change in flow rate of water when handle 110 is shifted from 50% to 100% of its range of motion is perceived as insignificant by the user.
Therefore, according to the current design of the cartridge and handle, only 25% to 50% of the range of motion of the handle from its closed position is used for fine adjustments of the flow rate. The remaining range of motion is typically not used for fine adjustments of the flow rate since the user usually does not need fine adjustments at the higher flow rates. The user may find it difficult to perform fine adjustments at the low flow rate range due the small range of motion used for these fine adjustments. This difficulty is further increased due to the friction force of the mechanical mechanism of the faucet that resists the movement and the inherent difficulty of a user to perform fine hand movements required to operate the prior art handle.